Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations that radiate to define wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
In general, a cellular wireless network may operate in accordance with a particular radio access technology or “air interface protocol,” with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or ranges of carrier frequencies In a frequency division duplex (FDD) arrangement, different carrier frequencies or ranges are used for the downlink than the uplink. Whereas, in a time division duplex (TDD) arrangement, the same carrier frequency or range is used for the downlink and uplink and is allocated over time among downlink and uplink communications.
Further, each coverage area may define a number of subsidiary air interface channels for carrying information between the base station and the UEs. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing, for instance. By way of example, each coverage area may define one or more downlink control channels and one or more downlink shared channels having resources that the base station may allocate on an as-needed basis to carry downlink communications to UEs, and each coverage area may provide a downlink reference signal that UEs can detect and measure as a basis to determine downlink channel quality. Further, each coverage area may define one or more uplink control channels and one or more uplink shared channels having resources that the base station may allocate on an as-needed basis to carry uplink communications from UEs, and each UE may provide an uplink reference signal that the base station may measure as a basis to determine a UE's uplink channel quality.
When a UE first powers on or enters into a base station's coverage area, the UE may “attach” with the base station, by transmitting an attach request to the base station. The attach request may cause the base station or associated infrastructure to authenticate and authorize the UE for service by the base station and to reserve network resources for use to serve the UE. In particular, the attach request may result in setup of one or more virtual bearer connections extending in the network between the base station and one or more transport networks and extending over the air interface as a radio link between the base station and the UE. Each such bearer may have a particular service level and intended use. For instance, one such bearer may be a default bearer for use to carry general data communications to and from the UE. Whereas, another such bearer may be a signaling bearer for use to carry packet-based session setup signaling such as Session Initiation Protocol (SIP) signaling between the UE and a network communication server, and another such bearer may be a dedicated bearer that provides a guaranteed minimum bit rate for carrying real-time media communications for instance.
Once the UE is attached with a base station, the UE may operate in a connected mode or an idle mode. In the connected mode, the UE may engage in communication of bearer data (e.g., application layer communications, such as SIP signaling, voice communication, video communication, file transfer, gaming communication, or the like), transmitting bearer data on uplink traffic channel resources to the base station and receiving bearer on downlink traffic channel resources from the base station.
Further, in the connected mode under some air interface protocols, the base station may manage scheduling of air interface resources (e.g., uplink and downlink shared channels) for use to carry communications wirelessly between the base station and the UE. For instance, each time the UE has data to transmit, the UE may send a scheduling request to the base station, and the base station may responsively signal to the UE to direct the UE to use certain uplink resources for the transmission. And each time the base station has data to transmit to the UE, the base station may similarly signal to the UE to direct the UE to receive the transmission on certain downlink resources. Alternatively, for certain types of communications, such as voice calls for example, the base station and UE may use a semi-persistent scheduling process in which certain periodic air interface resources are reserved for use to carry bearer data between the base station and the UE, without the need for the base station and UE to repeatedly exchange scheduling related signaling.
After a timeout period of no bearer data communication between the base station and the UE (possibly with respect to a particular bearer), or for other reasons, the UE may transition from the connected mode to the idle mode, with the base station releasing the radio link portion of one or more bearer connections assigned to the UE, so as to conserve air interface resources. In the idle mode, the UE may then simply monitor a downlink control channel to receive overhead information and to check for any page messages for the UE. Further, the UE may then engage in signaling with the base station to transition back to the connected mode if and when the UE receives a page message from the base station indicating an inbound bearer communication or if and when the UE seeks to engage in outbound bearer communication.
One increasingly important type of communication in cellular wireless networks is voice over Internet Protocol (VoIP) communication. In particular, as cellular wireless networks and associated UEs advance to support high quality IP based communication, wireless service providers that once provided voice telephony service using traditional PSTN connections will likely transition to support VoIP telephony service. To facilitate VoIP telephony service, a wireless service provider may make use of an Internet Multimedia Service (IMS) platform or the like, with which a served UE may engage in SIP signaling to set up VoIP communication, and through which the UE may then engage in VoIP communication to exchange voice with various remote telephony devices.